Motion translating apparatus



July 19, 1966 B. K. wooLFENDEN 3,261,216

MOTION TRANSLATING APPARATUS 5 Sheets-Sheet 1 Filed Sept. l2, 1965 ATTORNEYS Brian K /I/Bo/feno/en July 19, 1966 B. K. wooLFENDEN 3,261,216

MOTION TRANSLATING APPARATUS Filed Sept. l2, 1963 5 Sheets-Shea?l 2 INVENTOR.

ATTORNEYS July 19, 1966 B. K. wooLFENDEN 3,261,216

MOTION TRANSLATING APPARATUS 5 Sheets-Sheet 5 Filed Sept. l2, 1963 S x d l R ki l s INVENTOR. Brian .K Woofe/zo/en BY 06M, 7A/177W@ @mi www ATTORNEYS United States Patent O 3,261,216 MOTION TRANSLATING APPARATUS Brian K. Woolfenden, Grafton, N.H., assignor to Cryonetics Corporation, Burlington, Mass., a corporation of Delaware Filed Sept. 12, 1963, Ser. No. 308,434 4 Claims. (Cl. 74-60) The present invention relates to improvements in conversions of rotary to reciprocating motion, and, in one particular aspect, vto novel and improved inertia-compensated dry compressor apparatus in which pumping movements having advantageous reciprocating and rotational components are translated from shaft rotations through diaphragm sealing.

In the fluid pumping art, it has been well known to exploit the camming effects which can be produced by a non-rotating plate or ring which is so supported in bearings on a rotating drive shaft that it forms an acute angle with the drive shaft axis. Devices of this general character are commonly termed wobble-plate drives, and many of the pumps into which they are incorporated utilize spring-biased pumping bellows or the like which are adapted to be alternately compressed by the plate and expanded by their springs, thereby developing desired pumping cycles. Such bellows-type units do not well lend themselves to many applications because they tend to be limited in permissible stroke, pressure rating, and speed of operation. On the other hand, bellows-type pumping units readily afford hermetic sealing against contaminating substances which may -be present in certain portions of the equipment in which they are used; at low temperatures, such as are experienced in refrigeration applications, the freezing-out of such contaminants, particularly lubricants, can impair system operation.

Ditiiculties of the aforementioned character are readily overcome in accordance with the present teachings through exploitation of a unique form of motion-translating mechanism which eiciently converts drive shaft rotations into reciprocating motions attended by relatively minor angular oscillations. This motion-translating mechanism lends itself to low-cost and reliable construction, and to simple long-life diaphragm sealing of portions which are likely to be fouled by lubricants, especially under low-temperature conditions. In compressors involving counterbalanced arrays of positively-driven pistons operated by such mechanisms, relatively large pumping powers can be handled without serious vibration problems.

Accordingly, it is one of the objects of the present invention to provide novel and improved apparatus for conversions of rotary motion to reciprocating movements.

Another object is to provide unique motion-translating equipment of low-cost construction possessing mechanical niceties which are especially advantageous in the actuations of reciprocating parts such as pistons.

It is a further object to provide improved heavy-duty compressor apparatus having non-lubricated positivelydriven piston provisions and in which sources of contamination are isolated.

Still further, it is an object to provide refrigerant compressors capable of ecient high-power vibration-suppressed performance in which counterbalanced arrays of non-lubricated pistons are actuated through a unique sealed wobble-plate mechanism producing reciprocations of the pistons.

By way of a summary statement of practice of this invention in one of its aspects, a compressor for a refrigerant in the gaseous state is formed by two annular backto-back arrays of cylinder cavities angularly aligned so that the cooperating oppositely-disposed pistons may be paired on common piston rods, one at each end. The multiple piston-cylinder units are of a dry non-lubricated construction, including piston rings of material having 3,261,216 Patented July 19, 1966 self-lubricating characteristics, and this serves the purpose of avoiding such contamination of the gas streams as might otherwise occur upon freezing-out of conventional lubricants. arranged piston rods is mechanically coupled with a central wobble plate, each coupling being made by a nonlubricated ball-and-socket type universal joint centered eccentrically of the piston rod axis and near the periphery of the wobble plate. This plate is, in turn, mounted substantially at its center in bearings providing freedom for relative wobble movement of the plate on a drive shaft, the latter being rotated by a suitable motive device in other l frame-mounted bearings which permit its turning about an axis out of alignment with the skewed plate. Conventional flowable lubricants are used with the bearings carrying the more severe loadings of the shaft and wobble plate, and these are then fully isolated from the pumping sites and non-lubricated elements by a substantially flat circular diaphragm of pliable imperious material.

Although the features of this invention which are considered to be novel are set forth in the appended claims, further details as to preferred practices of the invention, as well as the further objects and advantageous thereof, may be most readily comprehended through reference to the following description taken in connection with the accompanying drawings, wherein:

FIGURE l represents a transversely cross-sectioned compressor embodying teachings of this invention, with some portions broken away to simplify the illustration;

FIGURE 2 provides an end view of the compressor of FIGURE 1, with cylinders removed and parts broken away to expose internal constructional details;

FIGURE 3 depicts an elementary for-m of improved motion-conversion mechanism;

FIGURE 4 is a transversely cross-sectioned view of a preferred compressor embodying the present teachings; and

FIGURE 5 portrays the apparatus of FIGURE 4 from the input shaft end, with -parts broken away to reveal certain details.

Compressor apparatus 6 illustrated in FIGURES l and 2 is of a type which may be used in the compression stage of `a refrigeration cycle, for example, and, for this purpose, includes a number of pistons, such `as piston 7, which are intended to be reciprocated within cooperating cylinders, such as cylinder unit 8, to develop the intended pumping effects. These 4cylinder -units are conveniently fabricated separately, and are then aflixed to a housing or framework 9 at the sites of side openings, such as the openings 10a-10e. Preferably, the frame openings and cylinders at the two sides of the housing are arranged annularly, and with angular alignments permitting each of the reciprocating piston shafts lla-llf to serve two oppositely-disposed pistons. The pistons need not all serve t-o pump in the same refrigeration loop, however, and certain of them may in fact serve passive or dummy roles where not needed for pumping purposes, although the double-ended arrangements of two pistons on each shaft -is advantageous in increasing the capacity of the apparatus without unduly increasing the overall size, and in maintaining piston rod alignments. In some constructions, the numbers of piston-cylinder units at each side may be different.

Advantageously, machines in which these teachings are practiced can be fully balanced, whether these machines are symmetrical or not, for example, by appropriate distribution of diametrically-opposed masses witnessed by the wobble plate, and by eccentrically disposing masses witnessed by the input shaft labout its axis of rotation.

Inlet and outlet valving, and relating piping connections, may be of common types which are not critically related to the inventive features here disclosed and which Importantly, each of the annularly-l are thus not separately described; as is well known, the cylinder heads -may be provided with small leaf-spring inlet valves and spring-loaded ballor plate-type outlet valves, for example. Motive power for the compressor is applied through input shaft 12 by a suitable electric motor, or the like, this shaft being supported in the housing on bearings 13a 'and 13b within a hub section 14. At its inner end, 12a, lthe drive shaft is sufficiently enlarged to receive in load bearings 15a and 15b a relatively rotatable axle 16 having its longitudinal axis 17--17 inclined at an acute angle 18 in relation to the axis of rotation 19-19 of shaft 12. Axle 16 serves to induce a wobble motion in a spider element 20, to which it is centrally secured by bolt 21, the arms 20a-201c of the spider element being angularly restrained about axis 17-17 because of their couplings with the piston shafts 11a-11], respectively. This relationship of parts is one which requires that 4the axle 16 wobble wi-th a nutational motion once about the center point 22, `at the intersection of shaft axes 17-17 and 19-19, without turning on its own axis 17-17, each time the drive shaft is forced to make one revolution by the associated external motive device (not illustrated). Each of the ends of the arms 20a-20]c of the spider element is correspondingly caused to traverse one full cycle of arcuate motion, about center point 22 and about a different axis therethrough normal to shaft axes 17-17 and 19-19. The cyclical arcuate movements, which are out `of phase with one another, are exploited in actuating the piston shafts into the required reciprocating motions for compressing purposes. In prior wobble-plate constructions known to me, compensation has been made for such arcuate movements by permitting certain rolling actions to occur or by permitting the piston shafts to deflect in the manner of a connecting rod. These techniques are of limited usefulness, in that the strokes must generally be kept relatively short, the rolling actions restrict positive wobble-plate thrusts to a single direction, and the needed freedom for piston shaft deflections prevents maximum structural integrity from being realized. By way of important distinction, the piston shafts 11a-1U are rigidly connected with the associated pistons, there being no need for wrist-pin pivoting or crank-shaft-type swinging movements; .at the same time, this more rugged and less costly construction accommodates relatively large piston strokes and achieves positive thrusts for both directions of piston reciprocations. These results are attained through use of speciallyarranged ball-and-socket-type universal c-ouplings, 23a- 237, a different one of these being located be-tween each of the ends of the spider arms 20a-20)c and a different one of the piston shafts 11a-1U- As shown in FIG- URES 1 and 2, the universal couplings are conveniently fabricated by forming spherically-surfaced ends or balls, 24a-24f, at the tips of the spider arms 20w-2072 respectively, and by mating these with metal cups 25a-2Sf of complementary internal configuration. These metal cups are made fast to the respective piston shafts 11a-11], as by brazing or the like, the centers 26a-26)c of these balland-socket-type assemblies being `similarly loca-ted eccentrically of the longitudinal axes of the piston shafts, as illustrated .in FIGURE 2. Spherically-contoured liners 27a-27)c are disposed between the ball-shaped spider arm ends and the metal receptacle cups, these liners being of a dry self-lubricated type such as lilled tetrafluoroethylene resin material. In operation, the eccentrically-disposed couplings cause reciprocati-ons of the pistons, attended by angular oscillations of the piston shafts and attached pistons, these angular oscillations being effected as the piston shafts are turned slightly about their longitudinal axes to permit the aforementioned angular excursions of the ends of the spider arms. The piston rings are also of a dry self-lubricated type, and, for example, the rings 23-30 (FIGURE 1) may be made of a filled tetrafluoroethylene resin for this purpose.

In compressors of the type under discussion it is highly desirable to avoid use orf greases or oils in these sites Where the refrigerant gas under compression may pick up 1min-nte amounts or vapiors and convey them to system locations where they may cause troublesome contaminations. Although advantageously dry self-lubricating materials are useful about the pistons and in the ball-andsocket couplings, the drive shaft bearings 13a and 13b 'and spider axle or crank bearings 15a and 15b are olf balllbearing types which must withstand relatively high loadings and frictions and are best served by the more conventional lubricants, such as greases or oils. Accordingly, the load-bearing assemblies are isolated from the remainder of the compressor by a flexible and substantially impervious annular sealing diaphragm 31. Inner peripheral portions of the diaphragm are tightly clamped in sealed relationship with the crank axle such that its center is about coincident with the center of wobble movement 22, and outer peripheral portions of the diaphragm are tightly clamped in sealed relationship with the housing hub 14. Preferably, diaphragm 3'1 is a fabric-reinforced elastomeric material, such as a nylon-reinforced rubber, which yields readily and remains pliable under repeated exure. The housing is thus divided into two chambers one of which is maintained gas-tight, while the other, containing the hub bearings, may be vented to the atmosphere.

Because of the confinements of piston shafts 11a-11]c laterally, a small amount of angular movement of each of ball ends of arms 20a-2G]c about crank axis 1;7-17 is required to er1-able these arms to make their wide angular excursions about axes normal to axis 17-17 and passing through cen-ter 22. As was noted hereinabove, the various spider arms 20a-20]c are -in out-orf-phase relationships in their angular excursions, and they are also out of phase in the small angular movements just referred to. Locking or jamming effects are avoided by permitting the spider arms to llex angularly about the axis 17-17 in response to these forces, and, for this purpose, the arms 20a-Ztl]c are made relatively thin in angular directions about crank axis 17-17. Flexure in the opposite langular directions, about axes normal to the crank axis through center 22, is undesirable, however, because piston thrust is developed through the arms i-n these directions, and the spider arms are thus made substantially thicker in these directions, as is shown by a comparison between the illustrations in FIGURES l and 2.

The motion-translating elements depicted in FIGURE 3 represent a basic form of the rotary-to-reciprocating conversion mechanism explica-ted in the structure of F IG- URES l and 2. Drive shaft 32 is rotated in one direction, 63, about axis 34-34 4by a suitable motive device (not shown) to produce cyclic longitudinal reciprocating motion of the output shaft 35 along its axis 36--36 This translation of movements is effected by an actuating arm 3'7 which is mounted on an enlarged crank section 38 of the shaft 32. Crank section 38 is substantially cylindrical, although its longitudinal axis 3-9-39 forms an acute angle 40 in relation to the drive shaft axis. Bearing unit 41 permits relative rotation of the drive shaft 32, while actuating arm 37 is held stationary about the drive sharft axis. The inclined relationship of the axes 39-39 and 34-34 promotes angular oscillations of actuating arm 37 about lanother axis, Ll2-4i2, which is normal to and intersects both of the other axes at a center o-f wobble-.like movement. Angular excursions olf arm 37 in the directions 43 'cause similar excursions of the integrally-formed ball member 44, and the latter, being mated with a socket or cup member 45 affixed to output shaft 35 eccentrically of its axis 36-36, causes the output shaft to be both pulled back and forth along its axis and angularly oscillated about the same axis. Bearing supports for output shaft 35 are not illustrated, nor for input shaft 32, although it will be understood that conventional forms of these are of course used to `guide the described movements. Importantly, the center 46 of the universal coupling provided by the ball-and-socket connection is displaced laterally from the output shaft axis 36-36, and normally lies outside orf the plane in which both sh-aft axes 36-36 and .34-34 are located. The latter condition is a limiting one, in that the system would become locked if the actuating anm and universal coupling were not disposed to project out of that plane during the operating cycles. Accordingly, the total effective length of the linkage between the two parallel shafts should always exceed the minimum distance between tihese shafts, and the dimensions .of and spacings between parts are selected to avoid brin-ging the universal center 46 into the same plane with the input and output shafts. 'Slight angular movements of the actuating arm 37 about the inclined crank ax'is 39-39 will also occur to accommodate the described output movements. Where the hnb 37a for arm 37 is angularly restrained about the crank axis, arm 37 must instead ex angularly about the crank axis, and it is then made sufficiently thin in that direction to provide such exure. The arm dimensions transversely to the directions of tlexure provide greater rigidity, however, to insure that the output shaft receives full thrusts needed to produce reciprocations of the out- .put shaft.

The preferred compressor embodiment 4S appearing in FIGURES 4 and 5 has general operating characteristics like those of the apparatus of FIGURES 1 and 2. Its input shaft 49 is rotated in a framework hub 50 about axis S1-51, `and a crank axle 52 is mounted within the input sharft for relative rotation about an axis 53-53 inclined lat an angle 54 in relation to the input sh'aft axis. Housing l55 provides a mounting for spaced annu-lar arrays orf cylinders, 56a--56d and 57a-57d, the pistons within these cylinders being fastened at opposite ends of the piston shafts, as in the illustrated case of piston shafts 58a and 58C. Dry self-lubricated piston rings 59-61 (FIGURE 4) seal the piston 62 with its cylinder 56a, and the other piston units are of like construction. O-ring or metallic resilient backing is preferably provided behind certain of the rings, such as the piston rin-gs 60 and 61, to promote tight sealing, the ring materiad being tetrauoroethylene resin or a like mate-ri-al having self-lubricated characteristics.

The four piston shafts involved in this structure are reciprocated along and simultaneously oscillated angularly about, their longitudinal axes, by action of a wobble plate unit 62 having four equally-spaced radial legs, two of which are designated 62a and 62e in FIGURE 4. This unit is firmly attached to crank axle 52, and describes the same nutational type of wobble motion referred to hereinbefore, about center 63, as lthe input shaft 49 is rotated. A pliant diaphragm seal 64, of impervious flexible material, preferably rubber which is fabric-reinforced, achieves the desired hermetic seal between the inner housing compartment 65 and the oilyor grease-filled hub 50. As illustrated in FIGURE 5, the housing or framework 55 may include provisions for various inlets 66a-66c and outlets 67a-67b in the compressor assembly. These, and the associated valving, are not specially related to the inventive featu-res under discussion, and may be of conventional form and arrangement, hence, are not further discussed.

The universal couplings existing between the respective legs of the wobble plate unit and piston shafts are also shown to be of the ball-and-socket-type. At the outer ends of legs `62a and 62C (FIGURE 4), cylindrical bosses 68a and 68e, respectively, are slidably mated with shafts, such as shaft 69a (FIGURES 4 and 5), with which the `balls 70a and 7 0c are fixed. These ball ends are socketed in metal receptacles 71a and 71C having liners 72a and 72e, respectively, which are of dry self-lubricated material such as a tetratluoroethylene resin. The linkage proportions and the relative positions of parts involved in the couplings between output (piston) shafts and crank axis 51-51 are as described hereinabove, and it should be noted, for example, that the centers 73a and 73e of the ball-and-socket couplings are eccentrically related to the piston shaft axes. Shaft-mounting (such as shaft 69a) of the ball ends 70a and 7Gb for sliding movements in bosses 68a and 68h enables the linkages to provide play which accommodates the slight angular displacements about axis 51-51 which must occur between the piston shafts 58a-58d and the actuating arms of the wobble plate unit. As shown in the detail appearing in FIGURE 5, the end 74 of ball shaft 69a is enlarged to lock it in relationship to arm 62a, and, further, the desired freedom for relative sliding movement between this shaft and the boss 68a is nevertheless inhibited 'by a spring 75 portrayed in the preferred form of a Belleville washer which occupies little space while developing very large thrusts. The springs preserve the linkages in an advantageously tight condition at all times during operation. The sliding movements occur wholly transversely to the directions of power transmission.

Based upon'these recognitions and teachings, motion conversion devices may be produced in a variety of sizes and forms, affording sealed transmissions of power with high efficiency. Although ball-and-socket couplings have been discussed in detail, known gimballed types of universal connections may instead by employed in other embodiments. Accordingly, it should be understood that the specific embodiments of the invention herein disclosed are intended to be of a descriptive rather than a limiting character, and various changes, combinations, substitutions, or modifications may be effected in practice of these teachings without departing either in spirit or scope from this invention in its broader aspects.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for pumping refrigeration fluid, comprising a housing including two chambers, a drive shaft supported in said housing in one of said chambers for rotation about an input axis by motive means, a plurality of pump cylinders mounted in said housing with their centers along a circular path concentric with ysaid input axis, pistons disposed in said cylinders, a different piston shaft connected with each of said pistons in the other of said chambers, the piston shafts `being slidable along pumping axes parallel with and equidistantly spaced from said input axis, dry non-lubricated piston rings of material having relatively low coeicient of friction sealing said pistons with said cylinders, actuator means in said other of said chambers mounted on said drive shaft in said one of said chambers for relative rotation about a crank axis inclined in relation to and intersecting said input axis at a center of wobble motion, said actuator means including a hub portion and a plurality of arms extending radially therefrom each at a different angular position in said other of said chambers, different universal joints coupling 4the ends of said arms with different ones of said piston shafts at a predetermined radial distance from said crank axis and at a predetermined lateral distance from said pumping axes thereof in said other of said chambers, dry self-lubricated plastic bearing material providing bearing surfaces in said universal joints, the sum of said predetermined radial and lateral distances in each connection being in excess of the distance between said input axis and said pumping axes, `bearing means lubricated with a moist lubricant mounting said actuator means on said drive shaft and disposed in said other of said chambers. an annular diaphragm of substantially impervious pliable material defining the separation between said chambers, means sealing the inner periphery of said diaphragm with said hub portion of said actuator means with the center of said diaphragm substantially coincident with said center of wobble motion, and means sealing the outer periphery of said diaphragm with said framework at a position wherein said diaphragm separates the sites of said plastic bearing material and said piston rings from the site of said bearing means lubricated with a moist lubricant, whereby rotation of said drive shaft results in out-of-phase reciprocations of said piston shafts and pistons, attended by angular oscillations of said piston shafts and pistons, while the moist lubricant is fully isolated from said other of said chambers by said diaphragm and is thereby prevented from freezing out in the refrigeration fluid.

2. Apparatus for pumping refrigeration fluids as set forth in claim 1 wherein said radially-extending arms of said actuator means are substantially rigid about axes normal to said crank axis and accommodate relatively small movements in directions angularly about said crank axis, whereby said arms ymay make relatively wide angularly excursions about axes normal to said crank axis and passing through said center of wobble motion without locking and jamming.

3. Apparatus for pumping refrigeration fluid-s as set forth in claim 2 wherein each of said arms is flexible in said directions .angularly 4about said crank axis.

4. Apparatus for pumping refrigeration lluids as set forth in claim 2 wherein each of said arms includes at the outer end thereof means slidable substantially in said References Cited by the Examiner UNITED STATES PATENTS 1,188,016 `6/1916 Slonecker 74-60 2,924,086 `2/1960 Fields 74-18..l X 2,935,365 5/1960 Dega 277-188 X 3,060,712 10/1962 Sisson 74-60 X MILTON KAUFMAN, Primary Examiner.

BROUGHTON G. DURHAM, Examiner.

F. E. BAKER, Assistant Examiner. 

1. APPARTUS FOR PUMPING REFRIGERATION FLUID, COMPRISING A HOUSING INCLUDING TWO CHAMBERS, A DRIVE SHAFT SUPORTED IN SAID HOUSING IN ONE OF SAID CHAMBERS FOR ROTATION ABOUT AN INPUT AXIS BY MOTIVE MEANS, A PLURALITY OF PUMP CYLINDERS MOUNTED IN SAID HOUSING WITH THEIR CENTERS ALONG A CIRCULAR PATH CONCENTRIC WITH SAID INPUT AXIS, PISTONS DISPOSED IN SAID CYLINDERS, A DIFFERENT PISTON SHAFT CONNECTED WITH EACH OF SAID PISTONS IN THE OTHER OF SAID CHAMBERS, THE PISTON SHAFTS BEING SLIDABLE ALONG PUMPING AXES PARALLEL WITH AND EQUIDISTANTLY SPACED FROM SAID INPUT AXIS, DRY NON-LUBRICATED PISTON RINGS OF MATERIAL HAVING RELATIVELY LOW COEFFICIENT OF FRICTION SEALING SAID PISTONS WITH SAID CYLINDERS, ACTUATOR MEANS IN SAID OTHER OF SAID CHAMBERS MOUNTED ON SAID RIVE SHAFT IN SAID ONE OF SAID CHAMBERS FOR RELATIVE ROTATION ABOUT A CRANK AXIS INCLINED IN RELATION TO AND INTERSECTING SAID INPUT AXIS AT A CENTER OF WOBBLE MOTION, SAID ACTUATOR MEANS INCLUDING A HUB PORTION AND A PLURALITY OF ARMS EXTENDING RADIALLY THEREFROM EACH AT A DIFFERENT ANGULAR POSITION IN SAID OTHER OF SAID CHAMBERS, DIFFERENT UNIVERSAL JOINTS COUPLING THE ENDS OF SAID ARMS WITH DIFFERENT ONES OF SAID PISTON SHAFTS AT A PREDETERMINED RADIAL DISTANCE FROM SAID CRANK AXIS AND AT A PREDETERMINED LATERAL DISTANCE FROM SAID PUMPING AXES THEREOF IN SAID OTHER OF SAID CHAMBERS, DRY SELF-LUBRICATED PLASTIC BEARING MATERIAL PROVIDING BEAR SURFACES IN SAID UNIVERSAL JOINTS, THE SUM OF SAID PREDETERMINED RADIAL AND LATEAL DISTASNCES IN EACH CONNECTION BEING IN EXCESS OF THE DISTANCE BETWEEN SAID INPUT AXIS AND SAID PUMPING AXES, BEARING MEANS LUBRICATED WITH A MOIST LUBRICANT MOUNTING SAID ACTUATOR MEANS LUBRICATED WITH A DRIVE SHAFT AND DISPOSED IN SAID OTHER OF SAID CHAMBERS. AN ANNULAR DIAPHRAGM OF SUBSTANTIALLY IMPERVIOUS PLIABLE MATERIAL DEFINING THE SEPARATION BETWEEN SAID CHAMBERS, MEANS SEALING THE INNER PERIPHERY OF SAID DIAPHRAGM WITH SAID HUB PORTION OF SAID ACTUATOR MEANS WITH THE CENTER OF SAID DIAPHRAGM SUBSTANTIALLY COINCIDENT WITH SAID CENTER OF WOBBLE MOTION, AND MEANS SEALING THE OUTER PERIPHERY OF SAID DIAPHRAGM WITH SAID FRAMEWORK AT A POSITION WHEREIN SAID DIAPHRAGM SEPARATES THE SITES OF SAID PLASTIC BEARING MATERIAL AND SAID PISTON RINGS FROM THE SITE OF SAID BEARING MEANS LUBRICATED WITH A MOIST LUBRICANT, WHEREBY ROTATION OF SAID DRIVE SHAFT RESULTS IN OUT-OF-PHASE RECIPROCATIONS OF SAID PISTON SHAFTS AND PISTONS, ATTENDED BY ANGULAR OSCILLATIONS OF SAID PISTON SHAFTS AND PISTONS, WHILE HE MOIST LUBRICANT IS FULLY ISOLATED FROM SAID OTHER OF SAID CHAMBERS BY SAID DIAPHRAGM AND IS THEREBY PREVENTED FROM FREEZING OUT IN THE REFRIGERATION FLUID. 